The Radio Receiver
Figure 1 illustrates the block diagram of a typical radio receiver. The front-end section amplifies via the Low Noise Amplifier (LNA) and downconverts (with the mixer) the signal from the antenna. The signal is filtered and then digitized, after which it is digitally processed for optimal signal quality and demodulator efficiency. The conditioned signal is then demodulated, and the demodulator's audio output is routed to the audio output of the radio.
Software Defined Radio (SDR)
As shown in Figure 1, all post ADC signal processing may be implemented via an SDR (Software defined radio) approach. For optimal efficiency and simplified design, some of the functions may be implemented in hardware in the front-end. This is especially true of wide bandwidth signal processing that may be easier to realize in hardware. In addition, decimation, which reduces the bandwidth of the interface between the front-end device and the SDR processor, can be implemented in the front-end to simplify the interface. In this case, any signal processing realized in the front-end must be sufficiently adaptable to avoid compromising the flexibility of the SDR backend.
In an ideal SDR implementation, any signal processing uniquely related to a particular standard should be implemented using SDR techniques. This enables a single radio front-end to be used with numerous broadcast standards through the SDR software.